To increase the recording density of a magnetic recording medium, a perpendicular magnetic recording technique has been contemplated as an alternative to the conventional longitudinal magnetic recording technique. A perpendicular magnetic recording medium uses a magnetic recording layer made of a hard magnetic material, and a backing layer made of a soft magnetic material that has a role of concentrating the magnetic flux generated by a magnetic head used for magnetizing (recording) the magnetic recording layer.
A perpendicular magnetic recording medium, however, has spike noise caused by magnetic domain walls formed in the soft magnetic layer that constitutes the backing layer. To reduce noise in a perpendicular magnetic recording medium, the formation of magnetic domain walls in the soft magnetic backing layer needs to be suppressed. In this respect, Japanese Patent Application Laid-open No. 6-180834 (paragraph no. 0029, FIG. 1), for example, uses a ferromagnetic layer of a Co alloy or the like, which is formed above or below the soft magnetic backing layer, that is magnetized in a desired direction to fix the magnetization thereof to control the formation of magnetic domain walls in a soft magnetic backing layer; Japanese Patent Application Laid-open No.10-214719 (paragraph no. 0009, FIG. 2)), for instance, uses an antiferromagnetic thin film with the magnetization thereof pinned using an exchange coupling technique.
In the above technique, the formation of magnetic domain walls can be suppressed through exchange coupling with the soft magnetic backing layer using an antiferromagnetic layer as a magnetic domain controlling layer, only if a sufficient exchange coupling is obtained. To obtain sufficient exchange coupling, however, as disclosed in the latter reference identified above, the soft magnetic backing layer needs to be heat treated to bring out the properties of the soft magnetic backing layer after the film formation. This heat treatment must be carried out for a long time while applying a magnetic field in the radial direction. Hence, this technique is not suited for mass production.
Moreover, with the technique disclosed in the former reference identified above, where a backing layer is formed by layering a soft magnetic layer and an antiferromagnetic layer a plurality of times, the structure of the backing layer becomes complex. Again, this technique is not suited for mass production.
Accordingly, there still remains a need for a perpendicular magnetic recording medium that has reduced noise while suited for mass production. The present invention addresses this need.